Process of color photography



Patented May 15, 1945 UNITED PROCESS OF COLOR PHOTOGRAPHY John Rau Weber, South River, N. 3., asslgnor to E. I. du Pont de Nemours & Company, Wilmlng ton, Del., a corporation of Delaware v No Drawing.

Application January 14, 1944, Serial No. 518,249

16 Claims.

(Cl. 95-88) a This invention relates to photography and more particularly to methods of producing photographic dye images. Still ;more particularly it relates to methods of color photography wherein dye images are produced by dye destruction processes. Still more particularly it relates to methods of color photography wherein dye images are produced in layers of photographic elements by the selective destruction of dyed layers by means of an imino-amino-methanesulflnic acid. The invention also relates to novel reducing compositions containing an imino-amino-methanesulfinic acid and another reducing agent capable of reducing exposed silver salts.

An object of this invention is to provide a photographic color process wherein diffusely dyed layers are locally'destroyed to form dye images. A further object is to provide such a method wherein dye images free from haze are formed. A still further object is to provide a new process for developing diffusely dyed silver halide layers and concomitantly destroying the dyes adjacent to the developed silver images. Another object is to provide such a method which can be carried out under weakly acid conditions. Another object is to provide new reducing compositions for obtaining reverse dye images by bleach-out methods of color photography. Yet another object is to provide a bleach-out process wherein economical reducing agents are used. Other objects are to provide new techniques for bleachout methods of color photography and to provide a general advance in the art. Still other objects will be apparent from the following description of the invention.

It has been found that the above objects may be obtained and a practical method of color photography provided by treating ,a diffusely dyed layer containing silver images with an aqueous solution containing an imino-amino-methanesulfinic acid. To be more specific, it has been found that photographic elements which contain one or more diffusely dyed, water-permeable, colloid layers which have silver images in contact with or adjacent to dyes, may be treated in an aqueous solution of an imino-amino-methanesulflnic acid to produce a dyestuff image. When the silver deposit and any remaining silver salts are removed, a dye image remains.

The silver deposits or images appear to act catalytically intensifying the bleaching action of the imino amino methanesulfinic acids and localizing their reducing or bleaching action on the dye at the silver image and in proportion thereto. The silver images may be formed prior to the bleaching or reducing action on the dyestuffs or substantially simultaneously therewith.

The expression an imino-amino-methanesulflnic acid is used to designate the oxygenated reaction products, e. g., of hydrogen peroxide and tion products.

thiourea and certain of its hydrocarbon substitu The exact structure of such oxygenated reaction products is not known with certainty. In the case of thiourea itself, the reaction product has been called thiourea dioxide by some investigators which is indicative of a formula such as that set forth in (A) below. Others, however, have advanced the name imino-aminomethanesulfinic acid and formamidine sulfinic acid which implies a structure having formula (B):

NH: 0 NH; 7 It is possible that both formulae may be equally correct, because the compound may exist in several desmotropic forms. It is possible that the compound exists in a desmotropic form wherein an equilibrium normally obtains between the two forms set forth above, which may undergo rearrangement depending upon whether the compound is in acid or alkaline medium, or upon physical characteristics such as temperature and pressure.

Furthermore, it is conceivable, considering the second formula, that it forms a salt when in alkaline solution, e. g. the sodium sulfinate when in sodium hydroxide solution. It is further conceivable that in acid solution it forms salts on the imino group, for instance a hydrochloride.

Since the utility of the compound in accordance with this invention does not depend upon the exact structure of the oxygenated reaction product of thiourea or hydrocarbon-substituted thiourea with hydrogen peroxide, and for convenience, the names imino-amino-methanesulfinic acid or formamidine sulfinic acid will be used. The expression, an imino-amino-methane sulfinic acid, will be used to cover formamidine sulfinic acid and its derivatives which are capable of reducing silver salts.

The process can'be used with any dyes which can be bleached or destroyed, e. g., with reducing agents such as sodium formaldehyde sulfoxylate, alkali stannites, sodium and potassium hydrosulfites, etc. For example, thevat dyes which are reduced into the leuco form; the so-called dianile dyes and equivalent dyes can be used. A class especially useful might be termed watersoluble, leuco-base-forming dyestufls.

In its preferred aspect, this invention consists in treating silver images in a layer of colloid binding material diffusely colored with a watersoluble, leuco-base-forming dyestuff, with an aqueous solution containing formamidine suffinic acid in the acid state for a time sufficient to bleach the dye in situ with the silver deposit. Since the greater density of the silver deposit represents the higher concentration of catalyst,

the diffuse dye layer is bleached most in these areas. Conversely, in the areas of least silver density the bleaching effect is least. Thus, after bleaching and removal of the silver deposit, a reverse dye image remains, i. e., where the silver is most dense the least dye remains, and vice versa. Thus, to produce a positive dye image, a layer containing a negative silver image and difiusely dyed is treated with the novel dye bleach baths of this invention.

When the process is to be effected under mildly alkaline conditions, it is desirable that a mild reducing agent be present. Thus, photographic developing agents, such as, for example, methylp-aminophenol sulfate, dlbromo-hydro-quinone, p-methyl-amino-o-cresol, 2:4 diamino phenol, can be advantageously combined with the iminoamino-methanesulflnic acid.

The invention will be further illustrated. but

is not intended to be limited by the following examples.

Example I A. Formamidine sulfinic acid grams 6.4 Sodium sulfite do 5.5 Water milliliters 1,000

B. Iodine grams 2.7 Potassium iodide do 5.5 Sulfuric acid (conc.) milliliters 84 Water do 1,000

The dye in contact with the silver image was bleached and the silver image itself was concomitantly partially removed. The weak silver image remaining after dye bleaching was removed with Farmers reducer, washed and dried. A yellow positive dye image was obtained, i. e., the dye image was a positive whereas the silver image had been a negative image.

Example II A gelatino silver halide emulsion was dyed with Pontamine Fast Green 5 BL (sold by E. I. du Pont de Nemours 8; 00., Wilmington, Del.) and exposed, developed and fixed in the manner known to the art. The dyed element was bleached in a formamidine sulfinic acid bath as described in Example I. The silver image present was removed by bleaching in a cupric chloride-potassium bromide followed by clearing in a 15% plain sodium thiosulfate solution. A reversed, greenish-blue dye image remained in the layer Example III A photographic element bearing a gelatino silver halide emulsion was dyed with a quantity of Pontamine Fast Pink BL, C. I. #353, and coated on a suitable support. After exposure, the image wasdeveloped to metallic silver and the element fixed and then treated with a solution consisting of:

Grams Formamidine sulfinic acid 20 Sodium sulflte 20 Water 1,000

As in the preceding examples, the dye was se-I lectively bleached at the points of contact with the silver image. The action of this solution is slower than the one used in the previous examples but produces a satisfactory dye image when the element is further processed as described in Examples I or II.

Example IV A fine-grain gelatino silver halide emulsion film such as is known in the trade as fine grain positive, (see J. S. M. P. E., vol. 34, No. 1, pp. 12 to 25) was dyed with a solution of Pontamine Sky Blue 6B (Schultz Number 510). On drying, the photographic element was exposed, developed and fixed in the manner known to the art. It was then treated with the following solution:

, Grams Formamidine sulfinic acid 20 Methyl-p-aminophenol sulfate 20.

Water 1,000

After removal of the weak silver image, a clear positive dye image remained.

Example V Grams Formamidine suliinic acid 20 Monomethyl-p-aminophenol sulfate 20 Sodium carbonate (10% solution) Water 1,000

After removal of the silver image, a clear reddishmagenta positive dye image remained.

In the preparation of the diffusely colored dyestuff layers in association with silver halides which have been described, various dyes may advantageously be employed. These are in general dispersed in the layers in theircolored form, but it may in many cases be more desirable to incorporate dye intermediates in the silver halide layers and cause the formation of the dye by suitable reactions directly in the layer, preferably after the exposure of the photographic element to light. It may also be of some advantage to expose, develop and fix a silver halide emulsion to provide a silver image and then dye the emulsion the appropriate color by soaking in a solution of the desired dye. In the former case the majority of the substantive acid azo-dyes, various basic dyes, alizarine dyes, vat dyes, etc. may be used.

)AS examples of such dyes there may be mentioned:

Azo Fuchsine B, C. I. #66

Heliotrope B (Schultz #494) Chlorantine Fast Red 7 BL, C. I. #278 Diamine Rose GN, C. I. #126 Pontamine Fas't Green GL' Pontamine Scarlet B, C. I. #382 Pontamine Fast Scarlet G Pontamine Diazo Scarlet A, C. I. #324a Pontamine Fast Orange 20L Pontamine Fast Orange EGL' Croceine Scarlet MOO, C. I. #252 I Made by E. I. du Pont de Nemours 8: (10., Wilmington, e r

Suitable additional dye intermediates are those shown, for example, in Gaspar U. S. Patent No.

2,071,688. In copending application Serial No. 412,340 now U. S. Patent 2,339,309 it is disclosed that silver halide layers containing a latent image can be preferentially reduced or developed by treatment with a bath containing an acid sulfite solution of formamidine sulfinic acid.

It has been further discovered that it is possible to treat a dyed silver halide emulsion containing a latent image with formamidine sulfinic acid in order to first develop the latent image and concomitantly bleach out the dye where the latent image is converted to metallic silver. In this manner, simultaneous development of a. latent image is carried out coactively with the bleaching of the dyestuff at the points of formation of the silver image. This type of bleaching action will be further illustrated by the process described in the following example.

Example VI Grams Formadine sulfinic acid 0.5 Potassium bromide 1 Sodium bisulfite 3 Water 100 The silver image produced by this treatment was then removed by Farmers reducer revealing a reversed dye image produced by the bleaching of the dyestuff where the silver image had been deposited by the development of the latent image.

Example VII A film was coated on one side with a red-sensitized silver halide emulsion difiusely dyed with Supranol Brilliant Red (Schultz Farbstafftabelen, 13th edition, vol. II, page 204) over the redsensitive layer was then coated a blue-sensitive emulsion dyed with Pontamine Yellow CH. The opposite side of the film was coated with an emulsion sensitized predominantly in the green region and containing a water-soluble, yellow filter dye such as Tartrazine O. The red dyed layer was exposed through a positive printed from a green separation negative. This exposure was made through the green sensitized emulsion and the film base with a red printing light. Th yellow dyed layer was exposed by blue light behind a positive separation made from the blue separation negative. The green-sensitive layer was exposed through the red separation negative by light transmitted by a Wratten B filter, i. e., green light. The film was developed in a solution similar to that described in Example VI, fixed and washed. The silver image of the greensensitive layer was then converted to a cyanblue image by floating the film with that layer face down on the surface of a cyan-blue toning bath. The silver was then removed from the two front layers by floating'the film with the two emulsion coats side down on thesurface of a Farmers reducer solution after which the film was washed and dried. By this means a threecolored positive was obtained from three color separation negatives produced by well-known methods.

In place of dyeing the silver halide layer, or the developed and fixed silver halide layer, the dye can be incorporated in a colloid layer positioned adjacent to the silver halide layer. It has been found that the catalytic effect of the silver image extends beyond the thin emulsion layer in which it is incorporated and into another thin layer of dyed colloid binding material coated directly over or directly beneath the silver halide layer or spaced therefrom by means of a thin, water-permeable, colloid layer. The diffusely dyed layers in all instances are coactive with the previously or simultaneously formed silver image.

It has further been observed that the degree of dispersity of the developed silver image has a pronounced effect on the relative catalytic action thereof. Thus, for the same silver density, fine grain. ultra-violet sound recording, positive emulsions appear more suitable for dye bleach-out processes employing formamidine sulfinic acid bleach baths than coarser-grained emulsions.

While the above examples exemplify the utility of formamidine sulfinic acid or imino-aminomethanesulfinic acid in the various procedures, the invention as previously stated is not limited to that specific compound. On the contrary, the homologues and'substitution products which have similar reducing powers can be substituted in whole or in part for the reducing agent of the examples. Thus, other N-hydrocarbon substituted imino-amino-rnethanesulfinic acids which are capable of reducing silver salts, can be used in the above-described procedures and compositions in similar amounts. Suitable substituents include lower alkyl groups, e. g., methyl and ethyl; aryl radicals, e. g., phenyl, chlorphenyl, etc. Suitable substituted compounds include N-methyl formamidine sulflnic acid, N-ethyl formamidine sulfinic acid, N-alkyl formamidine sulfinic acid, N-phenyl formamidine sulfinic acid and N-chlorophenyl formamidine sulfinic acid which can be made from the corresponding N-hydrocarbon substituted thiourea and hydrogen peroxide,

The amount of reducing agent used can be varied over a fairly wide range. In general, from about 0.5% to 3% by weight of the imino-aminomethanesulfinic acid may be present in the aqueous reducing solutions. In general, at higher concentrations a darker silver image is formed in the concomitantprocedure and a more intensive dye removal obtained. Amounts from (11.5 to 2.0%

by weight of the imino-amino-methanesulfinic 4 acids in respect to the final weight of the solution are preferred.

Part or all of the specific preservatives set forth in the above examples can be substituted by one or more other sulfites, bisulfites, etc, Suitable additional compounds of this type include lithium, ammonium, substituted ammonium and amine salts of sulfurous acid, e. g. triethanolamine-, morpholine-, tetramethylammonium-, and trimethylbenzyl-ammonium sulfites. A portion of the bisulfites can be replaced by sodium, potassium and ammonium bisulfites and meta bisulfites.

Similarly in place of the specific restrainers of the above examples which can be interchanged in any desired manner, can be substituted one or more other compounds of this type. Suitable other compounds include sodium, lithium and ammonium bromides, chlorides, and iodides.

Various other developing agents can be used in place of the specific ones described above and disclosed in Examples IV and V. For instance, 2 4-diaminophenol hydrochloride, dibromohydroquinone, methyl-p-amino-o-cresol and dimethylp-aminophenol sulfate. Dry reducing compositions of such and other developing agents conabove. chloride, silver bromide, silver iodide, silver chloride-bromide, and silver chloride-bromide-iodide,

'sulflnic acids to produce dry compositions.

The dye-bleaching solutions of this invention are useful with various types of film base materials'and do not have a deleterious effect thereon. Thus, cellulose derivative film bases, e. g; cellulose nitrate, acetate, 10811111058 ether and mixed cellulose ester film bases, as well as synthetic resin film supports such as polyvinyl acetals, linear superpolymers, e. g. nylons, .etc. may

form part of the elements treated.

Various types of silver halide emulsion layers may be treated as will be apparent from the For instance, simple and mixed silver gelatin emulsion layers, may be satisfactorily processed by the novel solutions and procedures hereof. These silver halides, which may be optically sensitized, can be dispersed in other than gelatin binding agents such as agar agar, albugara e? dye with an ueous solution containing an iminoamino-methanesulflnic acid.

4. A process for preparing colored images which comprises treating a photographic element containing a preformed silver image and a coactive diffusely dyed colloid layer with an aqueous solution containing an imino-amino-methanesulflnic acid and removing the silver image.

5. A process for preparing colored images which comprises treating a photographic element containing a preformed silver image and a coactive diffusely dyed colloid layer with an aqueous solution containing formamidine sulfinic acid and removing the silver image.

6. A process for preparing colored images which comprises treating ,a photographic element contalning a preformed silver image and a coactive' colloid layer dyed with a water-soluble, leucobase-forming dye with an aqueous'solution containing formamidine sulflnic acid and removi g the silver image.

7. A process for preparing colored images whi h comprises treating a photographic element cog; taining a silver image and a coactive difiusel dyed colloid layer with an aqueous solution containing a small amount of a strong acid and mins, synthetic resins, e. g. polyvinyl acetals, polyvinyl alcohol, water-sensitive polyamide resins and water-sensitive polycarboxylic acid esters of cellulose, etc.

The baths can be used over a fairly wide range of temperature commensurate with the softening characteristics ofthe binding agent of the layers undergoing treatment. In addition, they havea fairly long useful life throughout practical processing temperatures.

One of the most important advantages of the invention is that formamidine sulflnic acid is a much more energetic photographic reducing agent in both acid and alkaline solutions than are the preferred compounds suggested by the art.

As many apparently widely different embodiments of this invention may be made, without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments hereof except as defined by the appended claims.

I claim:

1. A process for preparing colored images which comprises treating a photographic element containing a silver image and a coactive diffusely dyed colloid layer with an aqueous solution containing an imino-amino-methanesulfinic acid.

2. A process for preparing colored images which comprises treating a photographic element containing a silver image and a coactive diffusely dyed colloid layer with an aqueous solution containing an imino-amino-methanesulfinic acid and removing the silver image.

3. A process for preparing colored images which comprises treating a photographic element containing a silver image and a coactive colloid layer dyed with a water-soluble, leuco-base-forming formamidine sulfinic acid.

8. A process which comprises treating a photographic element having an exposed Silver halide layer and a coactive diffusely dyed colloid layer with an aqueous solution containing an iminoamino-methanesulfinic acid and removin the silver deposits and silver salts.

9. A process which comprises treating a photographic element having an exposed silver halide layer and a coactive colloid layer dyed with a water-soluble, leuco-base-forming dye with an aqueous solution containing an imino-amino-methanesulfinic acid and removing the silver deposits and silver salts.

10. A process which comprises treating a photographic element having an exposed silver halide layer and a coactive diffusely dyed colloid-layer with an aqueous solution containing formamidine sulfinic acid and removing the silver deposits and silver salts.

11. A reducing composition comprising an imino-amino-methanesulfinic acid and a photographic developing agent.

12. A dry reducing composition comprising an imino-amino-methanesulflnic acid and a photographic developing agent.

16. .A dry reducing composition comprising formamidine sulfinic acid, a photographic developing agent. and a water soluble alkaline sulfite.

J OHN RAU WEBER. 

